Rong Shang

Reversible Intramolecular Coupling of the Terminal Borylene and a Carbonyl Ligand of [Cp(CO)2MnBtBu]

Cyclic complex 2 with bridging carbonyl ligands was synthesized from a facile and reversible intermolecular carbonyl-borylene ligand coupling reaction at room temperature. Complex 2 exhibits an unprecedented coordination mode for boron-metal complexes, which is also reflected in its remarkable (11)B NMR chemical shift of -57.2 ppm. Findings from spectroscopic, X-ray, and computational studies are presented, along with a proposed mechanism.

Reactivity of transition-metal borylene complexes: recent advances in B-C and B-B bond formation via borylene ligand coupling.

Terminal borylene complexes of group 6-10 metals have been prepared through a number of synthetic strategies, displaying a wide structural diversity with numerous coordination modes of the borylene ligand [:BR]. Earlier, amino-substituted borylenes were found to serve as borylene ligand transfer reagents to a range of organic and organometallic substrates. In contrast, aryl- and alkyl-substituted borylenes display metathesis behavior when combined with ketones. Recent studies on these complexes revealed new reactivity patterns involving borylene-borylene and carbonyl-borylene ligand coupling. Herein a brief account on the recent progress of these borylene ligand coupling reactions made in our laboratories is provided. These reactions offer unprecedented alternative methods for electron-precise B-B and B-C bond formation.

Isolation of the key intermediates of base-promoted borylene–carbonyl coupling reactions

The terminal alkylborylene complex [(η5–C5H5)(OC)2MnBtBu] (1) reacts with trimethylphosphine and CO to form a borylene–carbonyl coupling product [(η5–C5H5)(OC)Mn{κ2–C,C′–C(O)B(tBu)(PMe3)C(O)}] (3). This reactivity can be extended to nitrogen- and carbon-based ligands to form similar complexes [(η5–C5H5)(OC)Mn{κ2–C,C′–C(O)B(tBu)(L)C(O)}] (L = DMAP, 7, and IMe, 8). The key intermediates of these reactions were found to be neutral, Lewis base-stabilized borylenes of the form [(η5–C5H5)(OC)2MnB(tBu)(L)] (L = 4-dimethylaminopyridine (DMAP), 4, 3,5-lutidine, 5 and :C[N(Me)CH]2 (IMe), 6, which have been isolated and fully characterized. They can be synthesized from simple addition of the base to the parent borylene 1. The coordination of the base to the boron center seems to facilitate a rearrangement of the t-butyl borylene substituent.

Direct Conversion from Terminal Borylene into Terminal Phosphinidene

The first terminal manganese phosphinidene complex was quantitatively synthesized from a terminal alkylborylene complex. Its structure and bonding, as well as the reaction mechanism, were investigated through a combination of experimental and computational studies.